1. Technical Field of the Invention
This invention relates generally to electromagnetic transducers such as audio speakers, and more specifically to an improved frame and surround suspension configuration for such.
2. Background Art
FIG. 1 illustrates a conventional speaker 10 with an external magnet geometry motor structure 12 driving a diaphragm assembly 14. The motor structure includes a pole plate 16 style yoke, made of soft magnetic material and including a back plate 18 and a pole piece 20 that are either magnetically coupled or of integral construction. The pole plate may optionally include a ventilation hole 22 for depressurizing the diaphragm assembly. One or more external ring hard magnets 24 are magnetically coupled to the back plate. A top plate 26 of soft magnetic material is magnetically coupled to the hard magnets. A magnetic air gap 28 is formed between the top plate and the pole piece.
A frame or basket 30 is mechanically coupled to the motor assembly to support the diaphragm assembly. A diaphragm 32, sometimes referred to as a cone, is coupled to the basket by a flexible suspension component known as a surround 34. A voice coil former or bobbin 36 is mechanically coupled to the diaphragm, and is coupled to the basket by a flexible suspension component known as a spider 38. The surround and spider allow the bobbin and diaphragm to move axially with respect to the motor structure, but prevent, as much as possible, their lateral movement and rocking. An electrically conductive voice coil 40 is wound around and mechanically coupled to the bobbin, and is disposed within the magnetic air gap of the motor structure. A dust cap 42 is coupled to the diaphragm to seal the open end of the bobbin.
As illustrated in the detail view 1A, the surround includes a middle portion 44 such as a half-roll of flexible rubber, which provides the flexible suspension function of the surround. The surround also includes an inner portion 46 which is glued or otherwise coupled to the diaphragm 32, and an outer portion 48 which is glued or otherwise coupled to the frame 30. More specifically, the outer portion 48 of the surround extends radially outward, perpendicular to the axis of the speaker's motor structure, and is coupled to a similarly outward-extending flange 50 of the frame. The flange has a dimension sufficient to not only provide a large gluing surface for the surround, but also to accommodate the various mounting holes 52 which are used to couple the speaker basket to a baffle such as the front of an enclosure or a wall.
The suspending middle portion of the surround is not necessarily in the shape of a half-roll, but can be any suitable shape.
FIG. 2 illustrates that having these radially-extending components around the entire perimeter of the speaker limits the size of the diaphragm relative to the total outer dimension of the speaker, and limits the designer's ability to pack the diaphragms of multiple speakers in close proximity to each other on a common baffle. As shown in detail 2A, there is a considerable distance from the effective outer perimeter of one speaker's diaphragm 32a to the effective outer perimeter of the adjacent speaker's diaphragm 32b, because of the radially-extending outer surround components 46a and 46b, and because of the radially-extending frame flanges 50a and 50b, especially as the flanges must be wide enough to encompass the mounting holes.